The present invention relates generally to printers, such as ink jet printers, and, more particularly, to a priming system for priming a printhead.
The present invention relates generally to printers and, more particularly, to a priming system for priming a printhead, with the advantage, for example, that the system is faster than prior art systems.
A prior art ink jet printer of the so-called xe2x80x9cdrop-on-demandxe2x80x9d type has at least one printhead from which droplets of ink are directed towards a recording medium. Within the printhead, the ink can be contained in a plurality of channels and energy pulses are used to cause the droplets of ink to be expelled, as required, from orifices at the ends of the channels.
In a thermal ink jet printer, the energy pulses are usually produced by resistors, each located in a respective one of the channels, that are individually addressable by current pulses to heat and vaporize ink in the channels. As a vapor bubble grows in any one of the channels, ink bulges from the channel orifice until the current pulse has ceased and the bubble begins to collapse. At that stage, the ink within the channel retracts and separates from the bulging ink, which forms a droplet moving in a direction away from the channel, and towards the recording medium. The channel is then refilled by capillary action, which in turn draws ink from a supply container. Operation of a thermal ink jet printer is described in, for example U.S. Pat. No. 4,849,774, the disclosure of which is incorporated by reference in it entirety.
One particular form of thermal ink jet printer is described in U.S. Pat. No. 4,638,337. That printer is of the carriage type and has a plurality of printheads, each with its own ink supply cartridge, mounted on a reciprocating carriage. The channel orifices in each printhead are aligned perpendicular to the line of movement of the carriage and a swath of information is printed on the stationary recording medium as the carriage is moved in one direction. The recording medium is then stepped, perpendicular to the line of carriage movement, by a distance equal to the width of the printed swath and the carriage is then moved in the reverse direction to print another swath of information.
It is useful and effective to prime a printhead before initial use to ensure that the printhead channels are completely filled with ink and contain no contaminants or air bubbles. Current priming operations involve either forcing or drawing ink through the printhead and out the printhead nozzles, while a cap sealingly encloses the nozzles. Hoses or conduits are provided to remove the ink removed from the printhead during the priming operation. The most widely used priming technique for thermal ink jet printers is to subject the printhead nozzles to a vacuum or negative pressure to withdraw ink from the nozzles rather than to subject the printhead to pressure to force the ink from the nozzles. Accordingly, the maintenance station for a thermal ink jet printhead generally uses a vacuum pump to suck or draw ink from the printhead nozzles.
When priming a printhead, it is useful to apply a sharp vacuum profile to the face of the printhead, as this generally is more effective at removing air bubbles from an attached cartridge. More specifically, by applying a sharp vacuum profile, we can reach a peak vacuum rapidly, which generally is more effective at removing air bubbles. For example, previous vacuum priming systems have had a priming profile that reaches the peak vacuum in less than 0.1 seconds. Currently, a sharp vacuum profile is achieved by building a vacuum reservoir by means of an accumulator chamber and then rapidly applying the vacuum to the printhead by means of a pinch valve.
The following disclosures are mentioned:
U.S. Pat. No. 6,190,007 discloses a printhead carriage for an ink jet printer having a plurality of printhead stalls therein. An arcuately moveable air pump is engageable with one of a number of arcuately positioned inlets to the passageways in the carriage cover to enable a single pump to selectively apply positive pressure to prime each of the printheads in a desired sequence.
U.S. Pat. No. 6,174,052 discloses a priming system for ink jet printers, including an ink tank, an ink supply line, an ink bypass line and a valving arrangement that alternately permits either pressurized ink to be supplied to a remote printhead for printing purposes or unpressurized ink to be drawn to the printhead by use of a vacuum source applied to the bypass line. The printer nozzle valve is fitted with an ink bypass line to a source of vacuum. When it is desired to purge and/or prime the ink supply line and nozzle, the air pressure to, or the pump from, the ink supply tank is turned off and vacuum is applied to the bypass line. This sucks ink or solvent from the ink supply tank through the ink line into the nozzle valve and back to a reservoir for reuse or, alternatively, to an ink trap.
U.S. Pat. No. 6,070,961 discloses a priming station for an ink jet printer that includes an ink accumulator tank. In embodiments, the ink accumulator tank is connected between a printhead nozzle face capping member and a vacuum pump.
U.S. Pat. No. 5,555,461 discloses a vacuum pump operated by a drive means. The vacuum pump is connected to a cap by a flexible hose. To prime a printhead, a carriage, upon which a cartridge is removably mounted, is moved from a capped position towards a fixed support member until a pinch valve contacts the support member, causing the pinch valve to rotate against the flexible hose and pinch it closed. When the carriage is returned to the location where the nozzle face is capped, but the flexible hose is no longer pinched closed, i.e., in the capped position, the sealed cap internal recess is subjected to a negative pressure. The print cartridge remains at this position for about one second. The negative pressure begins to drop slightly due to the flow of ink. After about one second, the carriage then moves, breaking the cap seal and stopping the priming. The cap pressure drops and returns to ambient.
U.S. Pat. No. 5,432,538 discloses a valve for use in a maintenance station for an ink jet printer. The maintenance station has a carriage on which a cap that selectively seals the printhead nozzle is mounted. The carriage is movable in and relative to a fixed support member of the maintenance station. A flexible hose interconnects the cap with a pneumatic source for the removal of air and ink from the cap. The selective movement of the carriage towards and away from a wall of the support member pinches the flexible hose closed between them without requiring closely toleranced movement of the carriage.
U.S. Pat. No. 5,121,130 discloses a printhead assembly for a thermal ink jet printer having a plurality of printheads and ink supply paths carrying ink to the printheads. The ink in each supply path then passes to its respective printhead via a tank, the position of which relative to the printhead establishes the ink pressure at the printhead discharge orifices. The tank is vented so that any air separating out from the ink can be removed. Capping means is provided to cap the ink discharge orifices when the printhead is idle and to prime/clean the printhead when required.
The disclosures of all of the above references are hereby incorporated by reference in their entirety.
Embodiments of the present invention include a method for priming an ink jet printhead that includes first bringing a vacuum pump up to a minimum predetermined speed. The pump is fluidly connected to a capping mechanism or cap through a tube. The minimum predetermined speed of the pump depends upon the size of the pump and the diameter and length of the tube running to the cap. After the pump reaches the minimum predetermined speed, the cap is then sealingly engaged with the printhead. The cap is connected to the printhead for a period of time long enough to prime the printhead (approximately one to three seconds), and then the cap is disengaged from the printhead.
Embodiments of the present invention also include an apparatus for priming a printhead, including a printhead, a capping mechanism sealingly connected to the printhead so as to create an air tight seal around the printhead, a tube in direct fluid communication with the capping mechanism, the tube and the capping mechanism having a combined volume of, for example, from about 355 mm3 to about 455 mm3, and a vacuum pump in direct fluid communication with the tube.